How does a greenhouse work?

A:

Quick Answer

According to the Alaska Science Forum, a greenhouse works by trapping a volume of air inside the structure, and allowing the sun's energy to heat that air without allowing the wind to dissipate it. Over time, the air becomes hotter and hotter until it reaches substantially higher temperatures than the outside conditions. A similar effect is what makes the interior of a parked car so hot on a sunny day.

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When the sun's energy strikes a patch of earth, it heats up the ground. Outdoors, that heat is radiated into the column of air above the ground, where the prevailing winds and the relatively large volume of air above the warmed patch will dissipate the heat throughout the atmosphere. In a greenhouse, the volume of trapped air above the warmed surface is much smaller, allowing it to heat up much faster. Also, the wind cannot blow this air around and mix it with cooler air, and heat is prevented from dissipating. When the sun goes down, the roof of the greenhouse begins cooling first, allowing moisture from the air to condense on the plastic or glass panes. This helps thermally insulate the greenhouse, preventing infrared energy from radiating out and keeping the interior warm throughout the night.